Recovery of geothermal energy by means of underground nuclear detonations

ABSTRACT

Geothermal steam is generated by setting off an underground nuclear detonation above a naturally hot stratum of igneous rock and thereafter introducing water into the formation above the hot stratum which has been made permeable by the nuclear detonation.

9 1 a United States atent [151 3,640,336 Dixon Feb. 8, 1972 RECOVERY OFGEOTHERMAL [52] U.S.Cl ..165/l,60/26, 165/45, ENERGY BY MEANS OF 166/247UNDERGROUND NUCLEAR [51] Int. Cl ..F28f 13/12 0f 72 Inventor: Rod P.Dixon, Salt Lake City, Utah OTHER PUBUCATIONS [73] Assignee: The Unit dst t i America as Non-military uses of nuclear explosive" by Gerald W.represented by the United States Atomic Johnson and Harold Brown:Scientific American, Dec. 1918 Energy Comnfission Vol. 199 N0. 6-pp.29-35 Primary ExaminerCharles Sukalo [22] Ffled' June 1970Att0rneyRoland A. Anderson [2]] Appl. No.: 47,699

ABSTRACT Related US. Application Data Geothermal steam IS generated bysetting off an underground [60] Division of Ser. No. 795,190, Jan. 30,1969, Pat. No.

3,608,636, which is a continuation-in-part of Ser. No. 734,661, June 5,1968, and a continuation-in-part of 54l,8l0, Apr. 11, I966.

nuclear detonation above a naturally hot stratum of igneous rock andthereafter introducing water into the formation above the hot stratumwhich has been made permeable by the nuclear detonation.

1 Claims, 2 Drawing Figures msmaum elsrz 3640.336

Fig. l

INVENTOR.

ROD P. DIXON BY waqm RECOVERY OF GEOTHERMAL ENERGY BY MEANS OFUNDERGROUND NUCLEAR DETONA'IIONS CROSS-REFERENCE TO RELATED APPLICATIONSThis is a divisional application of application Ser. No. 795,190 filedJan. 30, 1969, now US. Pat. No. 3,608,636 issued Sept. 28, 1971, whichis a continuation-in-part of copending applications Ser. No. 541,810,filed Apr. 1 l, 1966, now abandoned, and Ser. No. 734,66l filed June 5,1968.

BACKGROUND OF THE INVENTION It is well known that a nuclear detonationunderground will create a cylinder or roofed-over chimney filled withbroken rock, normally with a void space at the top. This is broughtabout by a large, hot cavity filled with vaporized rock being createdabout the detonation point. The formation of the initial hot cavity asthe vaporized mass expands following the shock wave and the subsequentand progressive caving of the cavity roof and the formation of thecylinder of fragmented rock are very well known and do not requirefurther description. Such a cylinder of broken material contains chunksof fractured rock, which range randomly in size from sand grains to hugeboulders. Normally, there is a permeability between 25 percent and 40percent.

In such detonations radioactive elements are released in or as a resultof the detonation and thereafter may impart excessive radioactivity toproducts which are to be removed from the formation. If water is presentor subsequently enters a nuclearly detonated formation containingtritiated water or other water-soluble radioactive detonations products,the water itself then becomes excessively radioactive and unfit forinclusion in municipal water supplies or for other purposes where itsradiation may constitute an impermissible health hazard.

OBJECTS OF THE INVENTION It is accordingly one object of this inventionto provide a method for minimizing the hazards of radioactivecontamination which attend the fragmentation of geological formations byunderground nuclear detonations.

Another object of this invention is to use underground nucleardetonation in combination with strata of igneous rock naturally heatedin the formation to a temperature substantially above the boiling pointof water to recover geothermal energy.

Other objects will become obvious from the following description andclaims.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a vertical section through amineral formation in which an entry hole for a nuclear explosive hasbeen placed.

FIG. 2 is a vertical section through the formation shown in FIG. I afterthe nuclear explosive has been detonated showing the chimney formed fromthe detonation.

GENERAL DESCRIPTION OF THE INVENTION In carrying out this invention, anuclear explosive is detonated underground within a zone above hotigneous rock. The zone for the explosive is selected far enough belowground to be nonventing and far enough above the igneous rock so thatthe ambient temperature is too low to interfere with the functioning ofthe nuclear explosive. The nuclear explosive must form a chimney whichextends into a zone of rock having a temperature greater than 200 C.

Water is then introduced into the chimney, producing steam when it comesinto contact with the stratum of igneous rock. The steam produced iswithdrawn and is used as a source of energy.

If the steam generated in the first stage after the nuclear detonationcontains an excessive amount of radioactivity, it

tivit level which is acceptable for the intended use.

T e invention will be further described in the following example.

EXAMPLE As illustrated in FIGS. I and 2, a thermonuclear device 304 isdetonated under nonventing conditions beneath an aquifer 303 whichtraverses a geological formation above a stratum of igneous rock 306which is naturally heated to a temperature which is sufficient tovaporize water. If the temperature of the hot igneous stratum is suchthat a nuclear explosive device may properly function therein the devicemay be placed within or in the immediate vicinity of such a stratum andthere detonated, creating a chimney or cylinder of fragmented formationextending from said hot stratum upward. If the fragmented formation istraversed by an aquifer or underground stream 303, the water therefromdescends through the chimney 401 down to the hot stratum and isvaporized whereupon the steam may be withdrawn from an upper portion ofthe chimney through well 302 to be used at the surface for generation ofelectricity in a power plant 308 or for other useful work. If theaquifer bed downstream from the chimney permits excessive leakage ofsteam into the formation it may be sealed in a conventional manner, forinstance, by drilling a separate well at an appropriate downstreamlocation an injecting a cementitious or other sealing composition whichreduces any excessive porosity to an acceptable level so that the steamcan properly be recovered through well 302. If there is no subterraneanwater available in the formation, a surface stream may be diverted intothe chimney for evaporation.

If the temperature of the heated igneous rock is too high to permitproper functioning of the nuclear device in the immediate vicinitythereof, the desired result may be achieved by drilling a well 302 fromthe surface down to the hot stratum and thereafter placing anddetonating the device 304 in the well or entry means at a distance abovethe hot igneous stratum where the temperature of the surroundingformation is suitable, e.g., 200 C. or less. In this case, which is thecase specifically illustrated in FIGS. 1 and 2, the usual cylindricalchimney 401 is formed from the point of detonation upward but at thesame time the formation is also fragmented in a downward direction alongthe well 304 into the hot igneous rock 306 so that permeablecommunication is established therewith, as shown at 307. Thereafter whenwater is introduced into the fragmented chimney from the aquifer 303 orfrom an available surface source, steam is formed and recoveredtherefrom in the same manner as described earlier herein.

The scope of the invention is more in the appended claims.

What is claimed is: l. A process for producing steam in a formationwhich contains deep below the earth surface a stratum of igneous rocknaturally heated to a temperature above 200 C. with rock atprogressively lower temperatures thereabove, which process comprises:

drilling a hole down to said heated stratum, placing a nuclear explosivein an intermediate portion of said hole between said heated stratum andthe earth's surface at a depth sufficient to avoid venting of detonationproducts into the atmosphere and at a location where the temperature isless than 200 C.,

detonating said explosive and thereby creating a nuclearly detonatedchimney of fragmented rock reaching down to said heated stratum, f

introducing water into one portion of said fragmented chimney where itruns down and becomes vaporized,

and withdrawing 'steam from another portion of said chimney.

particularly pointed out

